The present invention relates to the field of asphalt paving and materials used therein.
Plant mix asphalt paving material uses rock and sand used which generally carry a negative charge which gives a stronger bond in between paving layers (i.e. opposite sides of magnets are attracted to one another). In the production of hot mix asphalt (HMA), heat is used to liquefy the asphalt so it will coat the aggregate and remain workable during transport, lay down, and compaction, as the asphalt cools, it hardens and regains the binding properties that make it an effective paving material.
When asphalt is milled into microscopic particles and dispersed in water with a chemical emulsifier, it becomes an asphalt emulsion. The tiny droplets of asphalt remain uniformly suspended until the emulsion is used for its intended purpose. In the emulsion state, the emulsifier molecules orient themselves in and around droplets of asphalt. The chemistry of the emulsifier/asphalt/water systems determines the dispersion and the stability of the suspension. When emulsions are used in the field, the water evaporates into the atmosphere, and the chemical emulsifier is retained with the asphalt. Asphalt emulsions are classified into three categories: anionic, cationic and nonionic. The anionic and cationic classes refer to the electrical charges surrounding the asphalt particles. This identification system stems from a basic law of physics: like charges repel one another and unlike charges attract.
In typical asphalt pavement structure, there are multiple layers. During paving, mechanical limitations prevent covering the entire surface area with a single pass of a paving machine. A typical road needs a minimal of two adjacent passes by the paving machine. The two passes create a joint between the asphalt laid, thus the strips of asphalt need to be bonded together to act as a single road surface. Joint sealant is the liquid material that is used to bond the two together. Tack coat is a very light spray application of asphalt emulsion. It is used to promote a bond between the existing surface and a new superjacent asphalt application. A tack coat is typically recommended for all overlays.
Tracking is defined as residual asphalt that sticks to the surface when a dump truck loaded with plant mix that will be dumped into the spreader backs across the tack coated treated surface and releases as it leaves the surface. Low tracking is very important where rapid adhesion is necessary. Examples include high traffic areas, where there is minimal traffic control, or where there is heavy truck traffic.